Since the mid-1990's so-called damascene processes have been the dominant technology for forming conductive interconnects in integrated circuits. Those skilled in the art recognize that damascene processing involves forming openings (via and trenches) in a dielectric layer and then filling the openings with a conductor, typically copper. The copper is typically deposited by initially depositing a thin seed layer within the openings and then filling the openings by electroplating copper.
FIG. 1 is a cross-sectional view of a prior art interconnect formed on a semiconductor device. In the figure, a patterned dielectric layer 54 is formed on a substrate 50. Formed within an opening of the patterned dielectric layer 54 and thereabove is a conductive layer 58. Formed between the dielectric layer 54 and the conductive layer 58 is a hard mask 56. A mask layer, such as a tri-layer photoresist layer 60 is formed above the conductive layer 58. In a later process, using the tri-layer photoresist layer 60 as a mask, the conductive layer 58 will be etched to form conductive lines 58 above the dielectric layer 54, as shown in FIG. 2.
The conventional copper metal line formation method can have a number of problems. One problem may be misalignment. In the process of device feature or pattern exposure, the alignment between successive layers that are being created is of critical importance. Smaller device dimensions place even more stringent requirements on the accuracy of the alignment of the successive layers that are superimposed on each other. In FIG. 2, following the etching of the conductive layer 58 in which the photoresist layer 60 is used as a mask to form conductive lines 58, via recesses VR may be formed at the juncture of a conductive line 58 and the hard mask 56 and/or the dielectric layer 54. Via recesses can be caused when the photoresist layer is misaligned (e.g., shifted to one side). Such misalignment can result from a mask misalignment failure, for example, during the photolithography process. Due to this misalignment, the via recess formed can be a serious problem in the conventional copper etch approach by causing unstable yield and decreased reliability.